A GaN crystal material is primarily used in conventional blue light and white light light-emitting diode (LED) products. A common technology for fabricating a light emitting layer is an epitaxial growth of the (0001) GaN crystal on a (0001) sapphire crystal or a (111) silicon substrate. Because the crystal plane (0001) (perpendicular to a c axis) of the GaN crystal is polar, according to common LED device structures, a polarity of a material may greatly reduce a quantum efficiency of the light emitting layer, thus greatly reducing a light emitting efficiency. Therefore, the quantum efficiency may be greatly raised by using a GaN LED device of a non-polar plane. However, a dislocation density of a GaN film, which has a non-polar a-plane or m-plane and is formed on the sapphire or silicon substrate by epitaxy, is a few orders of magnitude higher than that of the conventional (0001) GaN crystal because of factors such as lattice mismatch, so that it is difficult to apply the GaN LED device of the non-polar plane in a large scale production.
In addition, in a fabrication technology of a semiconductor device, it is generally needed to fabricate a specific crystal plane on a substrate to form a special three-dimensional structure. By coating a photoresist on a wafer substrate, transferring a planar pattern onto a photoresist mask by lithography, and then etching, a required structure such as a recess or a trench may be obtained with a conventional micro-fabrication technology. However, some special three-dimensional structures cannot be fabricated by the technology based on the planar process, and only some extremely special crystal planes, such as (111) of silicon, may be obtained by using an anisotropy characteristic of a wet etching. However, some crystal planes, such as (337), (5 5 12), (113), or (211) of silicon, cannot be fabricated on arbitrary orientation substrate.